The aim of the proposed study is to test the "glycoxidation hypothesis", which states that variations in oxidative stress among diabetic patients modulate the consequences of long-term hypoglycemia, specifically in determining the development of microvascular complications. The specific Aims are: To determine levels of glycoxidation products in skin collagen from complication-prone and complication-resistant diabetic patients (defined by retinopathy), and from non-diabetic control Using the data from control subjects to predict levels and rates of accumulation of glycoxidation products in skin collagen from individual diabetic patients, considering their long-term glycemic control, age and duration of diabetes. To compare predicted and actual levels and rates of accumulation of glycoxidation products in the two groups of diabetic patients, thereby deriving indices of relative long-term oxidative stress. According to the glycoxidation hypothesis, patients in the complication-prone group will have higher long-term oxidative stress than those in the complication-resistant group.